The Lockheed F-117 Nighthawk is a retired American single-seat, subsonic twin-engine stealth attack aircraft developed by Lockheed's secretive Skunk Works division and operated by the United States Air Force (USAF). It was the first operational aircraft to be designed with stealth technology.
The F-117 was based on the Have Blue technology demonstrator. The Nighthawk's maiden flight took place in 1981 at Groom Lake, Nevada, and the aircraft achieved initial operating capability status in 1983. The aircraft was shrouded in secrecy until it was revealed to the public in 1988. Of the 64 F-117s built, 59 were production versions, with the other five being prototypes.
The F-117 was widely publicized for its role in the Gulf War of 1991. Although it was commonly referred to as the "Stealth Fighter", it was strictly an attack aircraft. F-117s took part in the conflict in Yugoslavia, where one was shot down by a surface-to-air missile (SAM) in 1999. The U.S. Air Force retired the F-117 in April 2008, primarily due to the fielding of the F-22 Raptor. Despite the type's official retirement, a portion of the fleet has been kept in airworthy condition, and Nighthawks have been observed flying since 2009.
In 1964, Pyotr Ufimtsev, a Soviet mathematician, published a seminal paper titled Method of Edge Waves in the Physical Theory of Diffraction in the journal of the Moscow Institute for Radio Engineering, in which he showed that the strength of the radar return from an object is related to its edge configuration, not its size. Ufimtsev was extending theoretical work published by the German physicist Arnold Sommerfeld. Ufimtsev demonstrated that he could calculate the radar cross-section across a wing's surface and along its edge. The obvious and logical conclusion was that even a large aircraft could reduce its radar signature by exploiting this principle. However, the resulting design would make the aircraft aerodynamically unstable, and the state of computer technology in the early 1960s could not provide the kinds of flight computers which would later allow aircraft such as the F-117 and B-2 Spirit to stay airborne. By the 1970s, when Lockheed analyst Denys Overholser found Ufimtsev's paper, computers and software had advanced significantly, and the stage was set for the development of a stealth airplane.